138 THE REIGN OF LAW. 



ridge, or still more of any of the diving sea-fowl. 

 He will find that though in the case of most of 

 these birds the quickness of sight enables him 

 to see the strokes separate from each other, it 

 is utterly impossible to count them ; whilst in 

 some birds, especially in the Divers, as well as in 

 the Pheasant and Partridge tribe, the velocity is 

 so great that the eye cannot follow it at all, and 

 the vibration of the wings leaves only a blurred 

 impression on the eye. 



Our subject here, however, is not so much the 

 amount of vital force bestowed on birds, as the 

 mechanical laws which are appealed to in order to 

 make that force effective in the accomplishment of 

 flight. The elasticity of the air is the law which 

 offers itself for the counteraction of gravity. But 

 in order to make it available for this purpose, there 

 must be some great force of downward blow in 

 order to evoke a corresponding rebound in the 

 opposite, or upward direction. Now, what is the 

 nature of the implement required for striking this 

 downward blow ? There are many conditions it 

 must fulfil. First, it must be large enough in area 

 to compress an adequate volume of air ; next, it 



